package tree;

import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

public class BinaryTree {

    public static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode root = new TreeNode('4');
        root.left = new TreeNode('3');
        root.left.left = new TreeNode('2');
        root.right = new TreeNode('5');
        root.right.left = new TreeNode('6');
        root.right.right = new TreeNode('7');
//        root.right.right.right = new TreeNode('0');
        return root;
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    public void inOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        inOrder(root.left);
        System.out.print(root.val + " ");
        inOrder(root.right);
    }

    // 后序遍历
    public void postOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");
    }

    public static int nodeSize;

    /**
     * 获取树中节点的个数：遍历思路
     */
    public void size(TreeNode root) {
        if (root == null) {
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    public int size2(TreeNode root) {
        if (root == null) {
            return 0;
        }
        return size2(root.left) + size2(root.right) + 1;
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

    public void getLeafNodeCount1(TreeNode root) {
        if (root == null) {
            return;
        }
        if (root.left == null && root.right == null) {
            leafSize++;
            return;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    public int getLeafNodeCount2(TreeNode root) {
        if (root == null) {
            return 0;
        }
        if (root.left == null && root.right == null) {
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    /*
    获取第K层节点的个数 假设根节点是第 1 层
     */
    public int getKLevelNodeCount(TreeNode root, int k) {
        if (root == null || k < 1) {
            return 0;
        }
        if (k == 1) {
            return 1;
        }
        return getKLevelNodeCount(root.left, k - 1) + getKLevelNodeCount(root.right, k - 1);
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    public int getHeight(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        return (leftHeight > rightHeight ? leftHeight : rightHeight) + 1;
    }


    // 检测值为value的元素是否存在
    public TreeNode find(TreeNode root, char val) {
        if (root == null) {
            return null;
        }
        if (root.val == val) {
            return root;
        }
        TreeNode ret;
        if ((ret = find(root.left, val)) != null) {
            return ret;
        }
        if ((ret = find(root.right, val)) != null) {
            return ret;
        }
        return null;
    }

    //层序遍历
    public void levelOrder(TreeNode root) {
        if (root == null) {
            System.out.println("null");
            return;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        TreeNode tmp;
        while (!queue.isEmpty()) {
            if((tmp = queue.remove()) != null) {
                System.out.print(tmp.val + " ");
                queue.add(tmp.left);
                queue.add(tmp.right);
            }
        }
        System.out.println();
    }


    // 判断一棵树是不是完全二叉树
    public boolean isCompleteTree(TreeNode root) {
        if (root == null) {
            return true;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        TreeNode tmp;
        boolean flag = true;// true 表示 tmp 可以不为空
        while (!queue.isEmpty()) {
            if((tmp = queue.remove()) != null) {
                if(!flag) {
                    return false;
                }
                queue.add(tmp.left);
                queue.add(tmp.right);
            } else {
                flag = false;// 此后 tmp 只能为空
            }
        }
        return true;
    }
}